let matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
];

alert(matrix[1][1]);


let arr = [1, 2, 3];

alert(arr);

alert(String(arr) === '1,2,3');

alert([] + 1);
alert([1] + 1);
alert([1,2] + 1);
